Spontaneous discharge of norepinephrine-containing locus coeruleus (NE- LC) neurons was examined during the sleep-walking cycle (S-WC) in behaving rats. Single unit and multiple unit extracellular recordings yielded a consistent set of characteristic discharge properties. (1) Tonic discharge co-varied with stages of the S-WC, being highest during waking, lower during slow wave sleep, and virtually absent during paradoxical sleep. (2) Discharge anticipated S-WC stages as well as phasic cortical activity, such as spindles, during slow wave sleep. (3) Discharge decreased within active waking during grooming and sweet water consumption. (4) Bursts of impulses accompanied spontaneous or sensory-evoked interruptions of sleep, grooming, consumption, or other such ongoing behavior. (5) These characteristic discharge properties were topographically homogeneous for recordings throughout the NE-LC. (6) Phasic robust activity was synchronized markedly among neurons in multiple unit populations. (7) Field potentials occurred spontaneously in the NE-LC and were synchronized with bursts of unit activity from the same electrodes. (8) Field potentials became dissociated from unit activity during paradoxical sleep, exhibiting their highest rates in the virtual absence of impulses. These results are generally consistent with previous proposals that the NE-LC system is involved in regulating cortical and behavioral arousal. On the basis of the present data and those described in the following report (Aston-Jones, G., and F. E. Bloom (1981) J. Neurosci.1: 887–900), we conclude that these neurons may mediate a specific function within the general arousal framework. In brief, the NE-LC system may globally bias the responsiveness of target neurons and thereby influence overall behavioral orientation.